Sacrificial shorting straps for superconducting qubits

ABSTRACT

A technique relates to protecting a tunnel junction. A first electrode paddle and a second electrode paddle are on a substrate. The first and second electrode paddles oppose one another. A sacrificial shorting strap is formed on the substrate. The sacrificial shorting strap connects the first electrode paddle and the second electrode paddle; The tunnel junction is formed connecting the first electrode paddle and the second electrode paddle, after forming the sacrificial shorting strap. The substrate is mounted on a portion of a quantum cavity. The portion of the quantum cavity is placed in a vacuum chamber. The sacrificial shorting strap is etched away in the vacuum chamber while the substrate is mounted to the portion of the quantum cavity, such that the sacrificial shorting strap no longer connects the first and second electrode paddles. The tunnel junction has been protected from electrostatic discharge by the sacrificial shorting strap.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support under Contract No.:W911NF-10-1-0324 awarded by the Intelligence Advanced Research ProjectsActivity. The Government has certain rights to this invention.

BACKGROUND

The present invention relates to superconducting techniques, and morespecifically, to a sacrificial shorting strap for superconductingqubits.

Quantum computing employs resonant structures called qubits to storeinformation, and resonators (e.g., as a two-dimensional (2D) planarwaveguide or as a three-dimensional (3D) microwave cavity) to read outand manipulate the qubits. To date, a major focus has been on improvinglifetimes of the qubits in order to allow calculations (i.e.,manipulation and readout) to take place before the information is lostto decoherence of the qubits. Currently, qubit coherence times can be ashigh as 100 microseconds and efforts are being made to increase thecoherence times. One area of research with respect to increasingcoherence times is focused on eliminating material at the edges of thequbit (i.e., edges) in order to reduce the electric field in that area.The material in proximity to the qubit includes imperfections thatsupport defects known as two-level systems (TLS).

SUMMARY

According to one embodiment, a method of forming a protected tunneljunction is provided. The method includes forming a first electrodepaddle and a second electrode paddle on a substrate, where the firstelectrode paddle and the second electrode paddle oppose one another, andforming a sacrificial shorting strap on the substrate, where thesacrificial shorting strap connects the first electrode paddle and thesecond electrode paddle. The method includes forming the tunnel junctionconnecting the first electrode paddle and the second electrode paddle,after forming the sacrificial shorting strap, mounting the substrate ona portion of a quantum cavity, and placing the portion of the quantumcavity in a vacuum chamber. Also, the method includes etching away thesacrificial shorting strap in the vacuum chamber while the substrate ismounted to the portion of the quantum cavity, such that the sacrificialshorting strap no longer connects the first electrode paddle and thesecond electrode paddle, and placing the quantum cavity in a coolingchamber for operation. The tunnel junction has been protected fromelectrostatic discharge by the sacrificial shorting strap.

According to one embodiment, a system for protecting a tunnel junctionfrom electrostatic discharge when handling the tunnel junction. Thesystem includes a quantum cavity configured as a waveguide enclosure,and an assembly mounted to the quantum cavity. The assembly includes afirst electrode paddle and a second electrode paddle on a substrate,where the first electrode paddle and the second electrode paddle opposeone another. Also, the assembly includes the tunnel junction connectingthe first electrode paddle and the second electrode paddle, a firstlocation on the first electrode paddle, and a second location on thesecond electrode paddle. The first electrode paddle has a first raisedportion at the first location and the second electrode paddle has asecond raised portion at the second location. The first raised portioncorresponds to one end of a sacrificial shorting strap previouslyconnected at the first location on the first electrode paddle. Thesecond raised portion corresponds to another end of the sacrificialshorting strap previously connected at the second location on the secondelectrode paddle.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention. For a better understanding of the invention with theadvantages and the features, refer to the description and to thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The forgoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 is a top view of two paddles utilized to form a superconductingqubit on a substrate according to an embodiment;

FIG. 2 is a top view of a conductive, sacrificial shorting strap formedto connect the two paddles according to an embodiment;

FIG. 3 is a top view representing fabrication of the superconductingtunnel junction on the substrate according to an embodiment;

FIG. 4 is a cross-sectional view of superconducting tunnel junctionaccording to an embodiment;

FIG. 5A is a cross-sectional view of a first portion of a 3D quantumcavity with the substrate mounted to the cavity according to anembodiment;

FIG. 5B is a cross-sectional view of the second portion of the 3Dquantum cavity according to an embodiment;

FIG. 6 is a conceptual view of a vacuum chamber for removing thesacrificial shorting strap according to an embodiment;

FIG. 7 is a top view of the substrate after removing the sacrificialshorting strap according to an embodiment;

FIG. 8 is a top view illustrating that raised portions of the twopaddles may remain at the locations in which the shorting strappreviously contacted the paddles according to an embodiment;

FIG. 9 is a top view illustrating that remnants of the removed shortingstrap remains according to an embodiment;

FIG. 10 is a conceptual view of a cooling chamber housing the complete3D cavity according to an embodiment;

FIGS. 11A and 11B together illustrate a method of providing asacrificial shorting strap for protecting the tunnel junction of asuperconducting qubit according to an embodiment; and

FIG. 12 is a simplified version of cutting the sacrificial shortingstrap in two.

DETAILED DESCRIPTION

Three-dimensional (3D) superconductor qubits suffer from electrostaticdischarge effects, due to the antenna effect of its two large paddles,each of which is attached to opposite sides of a delicate tunneljunction.

State-of-the-art solutions include the use of a shorting strap which ismanually cut through immediately before testing, leaving one end of thesevered shorting strap attached to the one large paddle and the otherend of the severed shorting strap attached to the other large paddle.However, this process is not scalable and introduces particulates andlossy features into the qubit system. Particles of the cut shortingstrap are spewed onto and left on the two large paddles even inproximity to the delicate tunnel junction. Other lossy features incurredin this process include damage to the underlying substrate and residueleft from the severing process.

Embodiments present the use of sacrificial shorting straps (e.g.,niobium (Nb), which can be removed using a vapor etchant (e.g., XeF₂) ora wet etchant after processing and device mounting are completelyfinished. This eliminates the extraneous capacitance caused by theremnant shorting strap features (i.e., particles and/or severed shortingstraps attached to the two large paddles). As one example, a process forfabricating 3D superconducting qubits is to make aluminum (Al) paddlesand Al/AlO_(x)/Al tunnel junctions on a sapphire substrate. In such adevice, all components are resilient to XeF₂ etching according to anembodiment.

According to embodiments, the technique teaches the fabrication of aniobium (or other conductive material which can be etched by XeF₂ orother vapor etchant) shorting strap before the fabrication of theAl/AlOx/Al tunnel junction. Forming the sacrificial shorting strap canbe either before or after paddle formation. After junction fabrication,dicing, and mounting, the sacrificial shorting strap is then removedusing XeF₂.

FIG. 1 is a top view according to an embodiment. FIG. 1 illustrates asubstrate 100 with two paddles 5A and 5B according to an embodiment. Thesubstrate 100 may be, e.g., silicon, germanium, sapphire, etc.

A conductive layer may be deposited on top of the substrate 100, and thetwo paddles (pads) 5A and 5B are etched from the conductive layer. Thetwo paddles 5A and 5B may be made of a superconductive material, such asaluminum, titanium nitride, niobium, and/or niobium nitride.

Superconductivity is the phenomenon wherein the electrical resistance ofa metal disappears when the metal is cooled. Superconductivity occurs ina variety of metals, but only when they are cooled to extremely lowtemperatures, e.g., near absolute zero.

FIG. 2 is a top view according to an embodiment. FIG. 2 illustrates thata conductive (sacrificial) shorting strap 10 is formed to electricallyconnect paddles 5A and 5B. One end of the conductive shorting strap 10touches and/or is on top of the paddle 5A. The other end of theconductive shorting strap 10 touches and/or is on top of the paddle 5B.The conductive shorting strap 10 is an electrical shunt forelectrostatic discharge while providing a path to bypass the path of thedelicate tunnel junction (e.g., tunnel junction 40 shown in FIG. 3). Theshorting strap 10 may be formed by depositing the conductive materialand etching to the desired shape.

The conductive shorting strap 10 is made of a material that is highlyselectable for etching by an etchant while not etching other material asdiscussed further herein. In one implementation, the shorting strap 10may be a superconducting material such as, e.g., niobium (Nb), aluminum(Al), titanium nitride (TiN), niobium boride (NbB), where the strapmaterial can be etched selectively (compared) to other layers on thesubstrate 100. In the case of a superconducting strap, residue that isnot completely removed would not be lossy. In another implementation,the shorting strap 10 may be a material that is not superconducting butat least mildly conductive, such as, e.g., copper (Cu), silicon (Si),amorphous Si, or a conductive polymer, where the strap material can beetched selectively (compared) to other layers on the substrate 100 andwhich can be removed cleanly without residue.

As one example, when the substrate 100 is not silicon, e.g., thesubstrate 100 may be sapphire, the shorting strap 10 may be silicon, andthe etchant is configured to select silicon while not selecting theother layers on the substrate 100.

FIG. 3 is a top view representing fabrication of the superconductingtunnel junction 40 on the substrate 100. The superconducting tunneljunction 40 is connected to the paddles 5A and 5B via electrodes 20A and20B. The electrode 20A of the tunnel junction 40 is connected to andtouching paddle 5A, while the electrode 20B of the tunnel junction 40 isconnected to and touching paddle 5B.

The process of fabricating the superconducting tunnel junction 40 isunderstood by one skilled in the art. The superconducting tunneljunction (STJ), also known as a superconductor-insulator-superconductortunnel junction (SIS), is an electronic device consisting of twosuperconductors separated by a very thin layer of insulating material.Current passes through the junction via the process of quantumtunneling. The STJ is a type of Josephson junction and is part of thequbit. As an example, FIG. 4 is a cross-sectional view of the tunneljunction 40 according to an embodiment. FIG. 4 shows the electrodes 20Aand 20B sandwiching a thin insulator layer 25. The electrodes 20A and20B may be made of a superconducting material, such as aluminum (Al),titanium nitride (TiN), niobium (Nb), and/or niobium nitride (NbN). Inone implementation, the electrodes 20A and 20B may be made of the samesuperconducting material of the paddles 5A and 5B. The insulator layer25 may be an oxide such as, e.g., aluminum oxide (AlO) and/or siliconnitride (SiN).

The thickness (in the z-axis) of the electrodes 20A and 20B may be 50nanometers (nm) to 500 nm. The thickness of the insulator layer 25 issuch that, when separating the two superconducting electrodes 20A and20B, the insulator layer 25 is thin enough so that electrons canquantum-mechanically tunnel through the barrier, as understood by oneskilled in the art.

As noted above, three-dimensional (3D) superconductor tunnel junction 40can suffer from electrostatic discharge effects, due to the antennaeffect of the two large paddles 5A and 5B, each of which is attached toopposite sides of the delicate tunnel junction 40 via the electrodes 20Aand 20B. However, the shorting strap 10 has a lower resistance than thesuperconducting tunnel junction 40 thus allowing the shorting strap 10to act as an electrical shunt whenever electrostatic energy isdischarged between the paddles 5A and 5B, all while avoidingelectrostatic discharge through the high resistance tunnel junction 40.Accordingly, the substrate 100 can be physically handled by an operatorwithout blowing the insulator 25, because the electrostatic dischargeflows through the conductive shorting strap 10 instead. Blowing theinsulator layer 25 denotes forming holes in the insulator layer 25, thuspreventing the insulator layer 25 from performing as an insulator layer25. It is noted that the shorting strap 10 is not required to be ahighly conductive material, as long as the shorting strap 10 has a lowerresistance than the tunnel junction 40.

FIG. 5A illustrates a first portion 505A of the 3D cavity and FIG. 5Billustrates a second portion 505B of the 3D cavity. The first and secondportions 505A and 505B are each one-half of the 3D cavity, and bothhalves are attached together to form the 3D cavity (enclosure) asunderstood by one skilled in the art. The first and second portions 505Aand 505B may be attached together with screws, clamps, and/or any otherattaching device for microwave cavities as understood by one skilled inthe art. This is one example of a 3D cavity and one skilled in the artunderstands that there are other types of 3D cavities. The 3D cavity mayalso be referred to as a quantum cavity, microwave cavity, waveguideenclosure, etc., for controlling the frequency of the circuit on thesubstrate 100. The combined portions 505A and 505B may be an enclosedbox of a few centimeters or inches in length, width, and depth.

FIG. 5A shows the first portion 505A (e.g., one half) of the 3D cavitywith an input port 510A and an output port 510B for inputting andoutputting microwave signals to/from the substrate 100. In oneimplementation, the input port 510A and the output port 510B may befemale inputs for attaching coaxial cables. It is noted that thesubstrate 100 (with the layers forming a circuit) may be considered achip or assembly that has been diced for use. The substrate 100 ismounted to the first portion 505A across an elongated hole 520A withinthe first portion 505A. The substrate 100 may be mounted using screws oran adhesive.

FIG. 5B shows the second portion 505B (e.g., other half) of the 3Dcavity. The second portion 505B has an elongated hole 520B that matchesup with the elongated hole 520A in the first potion 505A, when the firstand second portions 505A and 505B are combined. Although the substrate100 (i.e., chip) is fixed to the first portion 505A, in oneimplementation, the substrate 100 may be fixed to the second portion505B across the elongated hole 520B. In another implementation, thesubstrate 100 may be fixed in the elongated hole 520A or 520B.

The first portion 505A and the second portion 505B are made of the samematerial. The first and second portions 505A and 505B of the 3D cavityare made of copper, for example.

FIG. 6 is a conceptual view of a vacuum chamber 600 for deposition ofmaterial and etching material. The vacuum chamber 600 includes one ormore inputs for inputting chemicals/materials and an output forevacuating chemicals/materials.

According to an embodiment, the first portion 505A containing thesubstrate 100 is placed in the vacuum chamber 600. The details of thesubstrate 100 are not shown for conciseness in FIGS. 5A, 5B, and 6, butit is understood that the substrate 100 includes the two large paddles5A and 5B, the electrode 20A and 20B, the tunnel junction 40, and theshorting strap 10 (along with a readout resonator (not shown) asunderstood by one skilled in the art).

In FIG. 6, an etchant 605 may be applied to the substrate 100 mounted tothe first portion 505A within the vacuum chamber 600. The purpose of theetchant 605 is to etch (i.e., remove) the conductive shorting strap 10while not affecting the substrate 100, the two large paddles 5A and 5B,the electrode 20A and 20B, and the tunnel junction 40 (along with thereadout resonator (not shown)). The conductive shorting strap 10 iscompletely removed from the substrate 100 while the substrate 100 ismounted to the first portion 505A. The first portion 505A, now servingas an alternative path to the tunnel junction 40, is able to dischargeany electrostatic electricity, and thus protects the tunnel junction 40while the shorting strap 10 is removed. Therefore, the substrate 100mounted to the first portion 505A can be physically handled by theoperator without risk of electrostatic discharge that would normallydamage the tunnel junction 40.

In one implementation, the etchant 605 may be a vapor etchant such as,e.g., XeF₂. In this case, the conductive shorting strap 10 may beniobium, tantalum, and/or silicon, and the XeF₂ removes niobium(tantalum or silicon) conductive shorting strap 10, without etching theother layers on the substrate 100.

In another implementation, the etchant 605 may be a wet etchant whosepurpose is to remove the conductive shorting strap 10 without etchingthe other layers. For example, an organic solvent may be used to removea conducting polymer as the conductive shorting strap 10 without etchingthe other layers on the substrate 100.

According to an embodiment, FIG. 7 illustrates the substrate 100 afterbeing removed from the vacuum chamber 600 and after being processed bythe etchant 605. At this point, the substrate 100 is still mounted onthe first portion 505A of the 3D cavity but the first portion 505A isnot shown for clarity. FIG. 7 shows that the conductive shorting strap10 has been removed. However, the tunnel junction 40 remains protectedfrom electrostatic discharge because of being mounted to the firstportion 505A of the 3D cavity.

According to another embodiment, FIG. 8 is a top view illustrating thatraised portions 805A and 805B of paddles 5A and 5B may remain at thelocations in which the conductive shorting strap 10 previously contactedthe paddles 5A and 5B. The raised portions 805A and 805B may be a resultof areas in the substrate 100 that did not endure the effects oflithography processing performed after the shorting strap 10 weredeposited. Fabrication processing of subsequent layers on the substrate100 bombards the previously formed paddles 5A and 5B, and thisbombardment of physical and chemical processing may reduce the thicknessof the paddles 5A and 5B in the z-axis. However, the raised portions805A and 805B were covered (i.e., protected) by the shorting straps 10during the bombardment, and thus the raised portions 805A and 805B arenot worn away as compared to areas of the paddles 5A and 5B that wereuncovered. In FIG. 8, the raised portions 805A and 805B are the actualmaterial of the paddles 5A and 5B but at a higher height in the z-axis.It is noted that the tunnel junction 40 and electrodes 20A and 20B arefabricated subsequent to the shorting strap 10. Additionally,fabrication of the readout resonator (not shown) may be subsequent tofabricating the shorting strap 10.

FIG. 9 illustrates locations 905A and 905B on the paddles 5A and 5B thatcontain remnants 10A and 10B of the shorting strap 10 itself accordingto an embodiment. The locations 905A and 905B are the places at whichthe shorting strap 10 contacted and covered the paddles 5A and 5B. Theremnants 10A and 10B of the shorting strap 10 were not completelyremoved during the etching process by the etchant 605, and thus remainon the paddles 5A and 5B. The material of the remnants 10A and 10B arethe same material of the removed shorting strap 10.

FIG. 10 is a conceptual view of a cooling chamber 1000. After theshorting strap 10 has been removed, the first and second portions 505Aand 505B are combined together to form the complete 3D cavity (alsoreferred to as a quantum cavity). The substrate 100 is still mounted onthe first portion 505A within the 3D cavity. The 3D cavity (theenclosure formed by first and second portions 505A and 505B) is placedinto the cooling chamber 1000 for operation and testing as understood byone skilled in the art. The cooling chamber 1000 represents a cryogenicchamber as understood by one skilled in the art.

FIGS. 11A and 11B are a method 1100 of providing a sacrificial shortingstrap 10 for protecting the tunnel junction 40 of a superconductingqubit according to an embodiment. Reference can be made to FIGS. 1-10.

At block 1105, the first electrode paddle 5A and the second electrodepaddle 5B are formed on the substrate 100, where the first electrodepaddle 5A and the second electrode paddle 5B oppose one another, asdepicted in FIG. 1.

At block 1110, the sacrificial shorting strap 10 is formed on thesubstrate 100 and the parts of the paddles 5A, 5B, and the sacrificialshorting strap 10 electrically connects the first electrode paddle 5Aand the second electrode paddle 5B, as depicted in FIG. 2.

At block 1115, the tunnel junction 40 is formed to electrically connectthe first electrode paddle 5A and the second electrode paddle 5B, afterforming the sacrificial shorting strap 10. The tunnel junction 40 haselectrodes 20A and 20B and insulator 25, as depicted in FIGS. 3 and 4.

At block 1120, the substrate 100 (e.g., a wafer diced into a chip) ismounted the on a portion (e.g., the first portion 505A and/or the secondportion 505B) of a quantum cavity, as depicted in FIGS. 5A and 5B.

At block 1125, the portion (e.g., first portion 505A and/or 505B) of thequantum cavity is placed in a vacuum chamber 600, as depicted in FIG. 6.

At block 1130, the sacrificial shorting strap 10 is etched away in thevacuum chamber 600 while the substrate is mounted to the portion (e.g.,first portion 505A and/or 505B) of the quantum cavity, such that thesacrificial shorting strap 10 no longer connects the first electrodepaddle 5A and the second electrode paddle 5B. The removal of thesacrificial shorting strap 10 is depicted in FIGS. 6 and 7.

At block 1135, the quantum cavity (combination of the first and secondportions 505A and 505B) is placed in a cooling chamber 1000 foroperation, and the tunnel junction 40 has been protected fromelectrostatic discharge by the now removed sacrificial shorting strap10, as depicted in FIG. 10.

When the substrate 100 is mounted on the quantum cavity in the vacuumchamber 600, an etchant 605 is utilized to etch away the sacrificialshorting strap 10 without removing the tunnel junction 40, the firstelectrode paddle 5A, and the second electrode paddle 5B.

The etchant is a wet etchant that does not attack the tunnel junction40, the first electrode paddle 5A, and the second electrode paddle 5B.In another case, the etchant 605 is a dry etchant that does not attackthe tunnel junction 40, the first electrode paddle 5A, and the secondelectrode paddle 5B. The dry etchant is XeF₂, for example.

When the substrate 100 is mounted on the quantum cavity in the vacuumchamber 600, an etchant 605 is utilized to etch away the sacrificialshorting strap, without requiring the sacrificial shorting strap 10 tobe cut in order sever the sacrificial shorting strap, as depicted inFIG. 12. When the substrate is mounted on the quantum cavity in thevacuum chamber 600, an etchant 605 is utilized to etch away thesacrificial shorting strap 10, without leaving the sacrificial shortingstrap 10 severed into a first part and a second part opposing eachother, as depicted in FIG. 12. FIG. 12 illustrates a simplified versionof cutting the sacrificial shorting strap 10 in two, while thesacrificial shorting strap 10 is mounted to the first portion 505A (notshown in FIG. 12). By using the technique discussed in embodiments, therequirement to cut the sacrificial shorting strap 10 while the tunneljunction 40 (not shown in FIG. 12) is already in place is no longernecessary, because the sacrificial shorting strap 10 is removed by theetchant 605.

The tunnel junction 40 is a Josephson junction. The tunnel junction 40comprises a first superconducting electrode 20A and a secondsuperconducting electrode 20B, where the first superconducting electrode20A and the second superconducting electrode 20B sandwich an insulatorlayer 25 as depicted in FIGS. 3 and 4.

The sacrificial shorting strap 10 prevents the insulator layer 25 in thetunnel junction from receiving the electrostatic discharge, thusprotecting the insulator layer 25 from becoming defective.

Before etching away the sacrificial shorting strap 10 in the vacuumchamber 600, one end of the sacrificial shorting strap 10 connects at afirst location on the first electrode paddle 5A and another end of thesacrificial shorting strap 10 connects at a second location on thesecond electrode paddle 5B. After etching away the sacrificial shortingstrap 10 in the vacuum chamber 600 while the substrate 100 is mounted tothe portion of the quantum cavity, the first electrode paddle 5A has afirst raised portion 805A at the first location and the second electrodepaddle 5B has a second raised portion 805B at the second location, asdepicted in FIG. 8. The first raised portion 805A and the second raisedportion 805B are material of the first electrode paddle 5A and thesecond electrode paddle 5B. The first raised portion 805A of thematerial has a higher height (in the z-axis) at the first location thanother areas of the material of the first electrode paddle 5A (i.e., theother areas are not at the location of the raised portion 805A). Thesecond raised portion 805B of the material has a higher height (in thez-axis) at the second location than other areas of the material of thesecond electrode paddle 5B (i.e., the other areas are not at thelocation of the second raised portion 805B). The one end and another endof the sacrificial shorting strap 10 covered the first location and thesecond location during formation of the tunnel junction 40, thus keepingthe material at the first location and the second location from wearingaway resulting in the first raised portion 805A and the second raisedportion 805B.

The first location includes a residual portion 10A of the sacrificialshorting strap 10, and the second location includes another residualportion 10B of the sacrificial shorting strap 10 as depicted in FIG. 9.The residual portion 10A and the other residual portion 10B of thesacrificial shorting strap 10 do not overhang from the first and secondelectrode paddles, respectively. For example, the residual portion 10Aand the another residual portion 10B in contrast to overhanging parts ofthe sacrificial shorting strap 10 in FIG. 12.

The quantum cavity is a three-dimensional cavity for operating thetunnel junction 40 within the cooling chamber 1000, as depicted in FIG.10.

It will be noted that various semiconductor device fabrication methodsmay be utilized to fabricate the components/elements discussed herein asunderstood by one skilled in the art. In semiconductor devicefabrication, the various processing steps fall into four generalcategories: deposition, removal, patterning, and modification ofelectrical properties.

Deposition is any process that grows, coats, or otherwise transfers amaterial onto the wafer. Available technologies include physical vapordeposition (PVD), chemical vapor deposition (CVD), electrochemicaldeposition (ECD), molecular beam epitaxy (MBE) and more recently, atomiclayer deposition (ALD) among others.

Removal is any process that removes material from the wafer: examplesinclude etch processes (either wet or dry), and chemical-mechanicalplanarization (CMP), etc.

Patterning is the shaping or altering of deposited materials, and isgenerally referred to as lithography. For example, in conventionallithography, the wafer is coated with a chemical called a photoresist;then, a machine called a stepper focuses, aligns, and moves a mask,exposing select portions of the wafer below to short wavelength light;the exposed regions are washed away by a developer solution. Afteretching or other processing, the remaining photoresist is removed.Patterning also includes electron-beam lithography.

Modification of electrical properties may include doping, such as dopingtransistor sources and drains, generally by diffusion and/or by ionimplantation. These doping processes are followed by furnace annealingor by rapid thermal annealing (RTA). Annealing serves to activate theimplanted dopants.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

1-16. (canceled)
 17. A system for protecting a tunnel junction fromelectrostatic discharge when handling the tunnel junction, the systemcomprising: a quantum cavity configured as a waveguide enclosure; anassembly mounted to the quantum cavity; wherein the assembly includes: afirst electrode paddle and a second electrode paddle both formed on anupper surface of a substrate, the first electrode paddle and the secondelectrode paddle opposing one another; the tunnel junction connectingthe first electrode paddle and the second electrode paddle, the tunneljunction formed on the upper surface of the substrate such that thetunnel junction, the first electrode paddle, and the second electrodepaddle are in a same plane; and a first location on the first electrodepaddle and a second location on the second electrode paddle, the firstelectrode paddle having a first raised portion at the first location andthe second electrode paddle having a second raised portion at the secondlocation, the first and second raised portion being material of thesubstrate; wherein the first raised portion corresponds to one end of asacrificial shorting strap previously connected at the first location onthe first electrode paddle; and wherein the second raised portioncorresponds to another end of the sacrificial shorting strap previouslyconnected at the second location on the second electrode paddle.
 18. Thesystem of claim 17, wherein the first raised portion and the secondraised portion are material of the first electrode paddle and the secondelectrode paddle.
 19. The system of claim 18, wherein the first raisedportion of the material has a higher height at the first location thanother areas of the material of the first electrode paddle; and whereinthe second raised portion of the material has a higher height at thesecond location than other areas of the material of the second electrodepaddle.
 20. The system of claim 17, wherein the first location includesa residual portion of the sacrificial shorting strap; wherein the secondlocation includes another residual portion of the sacrificial shortingstrap; and wherein the residual portion and the another residual portionof the sacrificial shorting strap do not overhang from the first andsecond electrode paddles, respectively.
 21. The system of claim 20,wherein the assembly is void of the sacrificial shorting strap such thatno sacrificial shorting strap connects the first electrode paddle to thesecond electrode paddle.